Historically, mechanical relays, vacuum tubes and gas discharge tubes have been utilized to control AC power where large voltage(e.g., &gt;100 volts) are involved. More recently, semiconductor switches have been developed employing bipolar transistors, field effect transistors and thyristors. Such semiconductor based switches have a number of well known limitations which are well known in the art. Among these limitations is the difficulty of providing the proper DC bias to the control lead of the semiconductor device. In the prior art this has generally been accomplished by providing a separate power supply for bias generation or by using a transformer to provide DC isolation of the control circuitry from the main AC power leads or a combination thereof. These and other prior art methods are bulky and costly and often fail to provide adequate isolation between the control and power leads of the switch.
Accordingly, it is an object of the present invention to provide an improved means for switching AC power using semiconductor elements, and which does not require external bias generation or use of a transformer for isolating the control input.
It is a further object of the present invention to provide an improved means for switching AC power using semiconductor elements and internal, transformerless, bias generation which does not require a common ground reference between power and control signals.
As used herein the words "switch" or "semiconductor switch" are intended to refer to a device employing semiconductor elements for continuously variable and/or binary (on-off) control of electrical power; the word "monolithic" is intended to refer to a structure that is formed on a common substrate in an integrated fashion rather than being assembled from separate independent parts; and the words "MOSFET" or "MOSFETS" are intended to refer to insulated gate field effect devices having either N or P type channels and various geometries.